I view Darkness controlled "undeveloped", planets are kinda like 'test groups' or 'public planets' used for the implementation of new features like creature spawning, bandit spawning, trophy drops and reclamation, hunting development, combat development, etc..
They are strewn across the galaxy and offer all players an opportunity to experience these parts of the game. Especially newer players without access to these resources on their own.

Unique stations are stations that exist somewhere on the game but cannot be reproduced by a group or a faction again. One of a kind, if you will..

Basically the admin controlled Darkness faction controls NPC homeworlds to prevent other players from building on and controlling them. They also control non-homeworlds that are used for testing (such as Derra) as well as temporary control when they take a planet from a faction as punishment.

The unique stations should be NPC owned to allow anyone to enter, but I suspect if they are Darkness owned it is because Jesfa just hasn't switched their ownership yet.